Add vpiTopModule

This patch adds functionality for vpiTopModule.

vpi_user.h

@@ -308,6 +308,7 @@ typedef struct t_vpi_delay  {
 #define vpiName       2
 #define vpiFullName   3
 #define vpiSize       4
+#define vpiTopModule  7
 #define vpiDefName    9
 #define vpiTimeUnit      11
 #define vpiTimePrecision 12

vvp/vpi_scope.cc

@@ -66,8 +66,12 @@ static int scope_get(int code, vpiHandle obj)
       switch (code) {
 	  case vpiTimeUnit:
 	    return ref->time_units;
+
 	  case vpiTimePrecision:
 	    return ref->time_precision;
+
+	  case vpiTopModule:
+	    return 0x0 == ref->scope;
       }
 
       return 0;